This proposal is an investigation of the interaction between behavioral dominance, behavioral stress, and levels of parasitemia. Hypotheses to be tested are: (1) Behavioral dominance status affects an individual's parasite load: (2) Parasite load can affect an individual's dominance status; (3) A dominance - subordinance relationship can be disrupted by the effects of parasites. All experiments will involve the use of even age male laboratory mice, and the parasitic nematode, Nematospiroides dubius.